Spraying material, spraying slurry, preparing method of spraying material, forming method of sprayed coating, sprayed coating, and sprayed member

ABSTRACT

A spraying material comprising a rare earth (R), aluminum and oxygen, the spraying material being a powder and comprising a crystalline phase of a rare earth (R) aluminum monoclinic (R4Al2O9) and a crystalline phase of a rare earth oxide (R2O3), with respect to diffraction peaks detected within a diffraction angle 2θ range from 10° to 70° by a X-ray diffraction method using the characteristic X-ray of Cu-Kα, the spraying material having diffraction peaks attributed to the rare earth oxide (R2O3) and diffraction peaks attributed to the rare earth (R) aluminum monoclinic (R4Al2O9), and an intensity ratio I(R)/I(RAL) of an integral intensity I(R) of the maximum diffraction peak attributed to the rare earth oxide (R2O3) to an integral intensity I(RAL) of the maximum diffraction peak attributed to the rare earth aluminum monoclinic (R4Al2O9) being at least 1.

CROSS-REFERENCE TO RELATED APPLICATION

This non-provisional application claims priority under 35 U.S.C. §119(a) on Patent Application No. 2019-076099 filed in Japan on Apr. 12,2019, the entire contents of which are hereby incorporated by reference.

TECHNICAL FIELD

This invention relates to a sprayed coating suitable for use as parts ormembers in a plasma etching apparatus which is employed in asemiconductor manufacturing process, and a forming method of a sprayedcoating, a spraying material or a spraying slurry used in the forming ofa sprayed coating, and a method of preparing a spraying material. Thisinvention relates also to a sprayed member suitable for use in a plasmaetching apparatus which is employed in a semiconductor manufacturingprocess.

BACKGROUND ART

In a plasma etching apparatus used in a semiconductor manufacturingprocess, a wafer to be processed is treated in a highly corrosive plasmaatmosphere of a halogen-based gas such as a fluorine-based gas or achlorine-based gas. Typically, fluorine-based gases such as SF₆, CF₄,CHF₃, ClF₃, HF and NF₃, and chlorine-based gases such as Cl₂, BCl₃, HCl,CCl₄ and SiCl₄ are used as the gases.

In a manufacturing of parts and members of a plasma etching apparatusexposed to a highly corrosive gas plasma atmosphere, generally, acorrosion-resistant sprayed coating is formed on the surface of asubstrate by an atmospheric plasma spraying (APS) method in which asource material such as a rare earth compound is supplied in powderform, or a suspension plasma spraying (SPS) method in which a sourcematerial dispersed in a dispersion medium is supplied in slurry form. Asthe rare earth compound, yttrium oxide, yttrium fluoride, yttriumoxyfluoride, and yttrium aluminum garnet are exemplified.

In sprayed coatings of the rare earth compound, yttrium oxide having agood corrosion-resistant to corrosive halogen-based gas plasma issuperior in plasma etching resistance, however, a sprayed coating of theyttrium oxide has a problem such that it has a large amount ofyttrium-based particles. It is considered that yttrium fluoride-basedcoating is superior in plasma resistance, however, has a comparably lowcoating hardness and is inferior in plasma etching resistance. Further,a yttrium aluminum garnet coating has advantages in a small amount ofrare earth particles and a high coating hardness, however, hasinsufficient corrosion resistance and is inferior in plasma etchingresistance.

Meanwhile, JP-A 2003-63883 (Patent Document 1) proposes a memberincluding a substrate and a mixed phase of a rare earth aluminummonoclinic phase, as a main phase, and at least one phase selected fromthe group consisting of a rare earth aluminum perovskite, a rare earthaluminum garnet and a rare earth oxide, as a sub phase laminatedthereon. However, it has room to be improved, particular, in a viewpointof corrosion resistance.

CITATION LIST

Patent Document 1: JP-A 2003-63883 (US 2003/0049500 A1)

DISCLOSURE OF INVENTION

For a corrosion-resistant sprayed coating used in parts or members in aplasma etching apparatus, a plasma resistant coating such as an yttriumoxide sprayed coating, an yttrium fluoride sprayed coating and anyttrium aluminum garnet coating was conventionally used. However, theconventional coating has a problem of insufficient plasma etchingresistance since the conventional coating generates a large amount ofyttrium-based particles by a reaction with corrosive halogen-based gasplasma, and has low hardness or low corrosion resistance.

An object of the invention is to provide a sprayed coating having highcorrosion resistance used for parts or members in a plasma etchingapparatus and having superior plasma etching resistance with reducedamount of particles generated by a reaction with halogen-based gasplasma, and a forming method of the sprayed coating. Another object ofthe invention is to provide a spraying material or a spraying slurry,and a preparing method thereof that is formable such a sprayed coating,and a sprayed member including such a sprayed coating.

The inventors have found a powdery spraying material containing a rareearth (R), aluminum and oxygen, including a crystalline phase of a rareearth (R) aluminum monoclinic (R₄Al₂O₉) and a crystalline phase of arare earth oxide (R₂O₃), and having a prescribed structure andprescribed properties The spraying material can form a sprayed coatinghaving high corrosion resistance and superior plasma etching resistancewith reduced amount of particles generated by a reaction withhalogen-based gas plasma. Further, the inventors have found the sprayingmaterial or a spraying slurry including the spraying material can besuitably prepared by the steps of forming a slurry by dispersing analuminum oxide in an aqueous solution of a rare earth salt; crystalizinga precursor containing the rare earth and aluminum, as a precipitate, byadding a precipitant to the slurry; collecting the precipitate by asolid-liquid separation; and firing the precursor containing the rareearth and aluminum under an oxygen-containing gas atmosphere.

Moreover, the inventors found that a sprayed coating including acomposite oxide containing the rare earth and aluminum can be formed bya thermal spraying, particularly, a plasma spraying with the sprayingmaterial or spraying slurry; particularly, the sprayed coating formed byusing the spraying material or spraying slurry contains a rare earth(R), aluminum and oxygen, and includes a crystalline phase of thecomposite oxide containing the rare earth and aluminum, having a rareearth-rich composition compared to the stoichiometric composition ofrare earth aluminum monoclinic (R₄Al₂O₉), and having a structure suchthat Al atom sites in the rare earth aluminum monoclinic (R₄Al₂O₉) arepartially substituted with the rare earth (R) atoms. The sprayed coatinghas high corrosion resistance and superior plasma etching resistancewith reduced amount of particles generated by a reaction withhalogen-based gas plasma. Further, the inventors found that a sprayedmember in which the sprayed coating is formed directly or via anunderlaying coating on a substrate is excellent for parts or members ina plasma etching apparatus.

In first aspect, the invention provides a spraying material containing arare earth (R), aluminum and oxygen, the spraying material being apowder and including a crystalline phase of a rare earth (R) aluminummonoclinic (R₄Al₂O₉) and a crystalline phase of a rare earth oxide(R₂O₃), wherein

with respect to diffraction peaks detected within a diffraction angle 2θrange from 10° to 70° by a X-ray diffraction method using thecharacteristic X-ray of Cu-Kα, the spraying material has diffractionpeaks attributed to the rare earth oxide (R₂O₃) and diffraction peaksattributed to the rare earth (R) aluminum monoclinic (R₄Al₂O₉), and

an intensity ratio I(R)/I(RAL) of an integral intensity I(R) of themaximum diffraction peak attributed to the rare earth oxide (R₂O₃) to anintegral intensity I(RAL) of the maximum diffraction peak attributed tothe rare earth aluminum monoclinic (R₄Al₂O₉) is at least 1.

Preferably, the spraying material has a BET specific surface area S ofat least 1 m²/g, and a bulk density ρ of up to 2 g/cm³. Particularly,the spraying material has a value S/ρ of 1 to 4, the value S/ρ beingobtained by dividing the BET specific surface area S by the bulk densityρ.

Preferably, the spraying material has a composition corresponding to arelative rare earth oxide (R₂O₃) content of 75 to 99 wt % and a relativealuminum oxide (Al₂O₃) content of 1 to 25 wt % in the total content ofthe rare earth oxide (R₂O₃) and the aluminum oxide (Al₂O₃), the rareearth oxide (R₂O₃) content and the aluminum oxide (Al₂O₃) content being,respectively, calculated from the basis of an rare earth (R) content andan aluminum content in the spraying material.

Preferably, the rare earth (R) in the spraying material is selected fromthe group consisting of yttrium (Y), gadolinium (Gd), terbium (Tb),dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium(Yb), and lutetium (Lu).

Preferably, the spraying material the spraying material has an averageparticle size D50 of 1 to 50 μm.

In second aspect, the invention provides a spraying slurry including thespraying material, and a dispersion medium, wherein a content of thespraying material in the spraying slurry is 10 to 70 wt %.

Preferably, the dispersion medium is an aqueous dispersion medium.

Preferably, the spraying slurry includes a dispersing agent.

Preferably, the spraying slurry has a viscosity of less than 15 mPa·s.

In third aspect, the invention provides a method of preparing a sprayingslurry including the steps of:

forming a slurry by dispersing an aluminum oxide in an aqueous solutionof a rare earth salt;

crystalizing a precursor containing the rare earth and aluminum, as aprecipitate, by adding a precipitant to the slurry;

collecting the precipitate by a solid-liquid separation; and

firing the precursor containing the rare earth and aluminum under anoxygen-containing gas atmosphere.

In fourth aspect, the invention provides a method of forming a sprayedcoating including the step of:

forming the sprayed coating including a composite oxide containing arare earth and aluminum, directly or via an underlaying coating on asubstrate by plasma spraying with using the spray material or thespraying slurry.

In fifth aspect, the invention provides a sprayed coating containing arare earth (R), aluminum and oxygen, the sprayed coating including acrystalline phase of a composite oxide containing the rare earth (R) andaluminum, wherein

the crystalline phase of a composite oxide includes a crystalline phaseof a composite oxide having a rare earth-rich composition compared tothe stoichiometric composition of rare earth aluminum monoclinic(R₄Al₂O₉), and having a structure such that Al atom sites in the rareearth aluminum monoclinic (R₄Al₂O₉) are partially substituted with therare earth (R) atoms.

Preferably, the sprayed coating includes a crystalline phase of a rareearth oxide (R₂O₃).

Preferably, the sprayed coating includes at least one crystalline phaseselected from the group consisting of a rare earth aluminum monoclinic(R₄Al₂O₉), a rare earth aluminum perovskite (RAlO₃), and a rare earthaluminum garnet (R₃Al₅O₁₂).

Preferably, the sprayed coating has a composition corresponding to arelative rare earth oxide (R₂O₃) content of 75 to 99 wt % and a relativealuminum oxide (Al₂O₃) content of 1 to 25 wt % in the total content ofthe rare earth oxide (R₂O₃) and the aluminum oxide (Al₂O₃), the rareearth oxide (R₂O₃) content and the aluminum oxide (Al₂O₃) content being,respectively, calculated from the basis of an rare earth (R) content andan aluminum content in the sprayed coating.

Preferably, the rare earth (R) in the sprayed coating is selected fromthe group consisting of yttrium (Y), gadolinium (Gd), terbium (Tb),dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium(Yb), and lutetium (Lu).

Preferably, the sprayed coating has a surface roughness Ra of up to 8μm, a thickness of 10 to 500 μm, a Vickers hardness HV 0.3 of at least600, and/or a porosity of up to 5%.

In sixth aspect, the invention provides a sprayed member including thesprayed coating formed directly or via an underlaying coating on asubstrate.

Advantageous Effects of Invention

According to the invention, a sprayed coating having superior plasmaetching resistance and high corrosion resistance with reduced amount ofparticles generated by a reaction with halogen-based gas plasma can beformed. The sprayed coating is excellent as a sprayed coating formed inparts or members of a plasma etching apparatus which is employed in asemiconductor manufacturing process.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an X-ray diffraction profile of the spraying material obtainedin Example 2.

FIG. 2 is an X-ray diffraction profile of the sprayed coating obtainedin Example 8.

DESCRIPTION OF PREFERRED EMBODIMENTS

A spraying material of the invention is suitable for forming, typicallyby thermal spraying such as plasma spraying, a sprayed coating (athermal sprayed coating) as parts or members in a plasma etchingapparatus which is employed in a semiconductor manufacturing process.The spraying material of the invention preferably contains a rare earth(R), aluminum and oxygen, and includes a crystalline phase of acomposite oxide containing a rare earth (R), aluminum, and, morepreferably, includes a crystalline phase of a rare earth (R) aluminummonoclinic (R₄Al₂O₉) and a crystalline phase of a rare earth oxide(R₂O₃). The spraying material of the invention is normally powdery(particulate). The spraying material of the invention can form a sprayedcoating having superior plasma etching resistance (corrosion resistance)with reduced amount of rare earth particles caused by corrosivehalogen-based gas plasma.

With respect to diffraction peaks detected within a diffraction angle 2θrange from 10° to 70° by a X-ray diffraction method using thecharacteristic X-ray of Cu-Kα, the spraying material of the inventionmay have diffraction peaks attributed to the rare earth oxide (R₂O₃) anddiffraction peaks attributed to the rare earth (R) aluminum monoclinic(R₄Al₂O₉), and an intensity ratio I(R)/I(RAL) of an integral intensityI(R) of the maximum diffraction peak attributed to the rare earth oxide(R₂O₃) to an integral intensity I(RAL) of the maximum diffraction peakattributed to the rare earth aluminum monoclinic (R₄Al₂O₉) is preferablyat least 1, more preferably at least 1.1. An upper limit of theintensity ratio I(R)/I(RAL) is normally up to 45. The integral intensitymay be obtained by integrating intensities in the peak (integratingwithin the peak area) from the resulting XRD profile (diffractionintensity profile). In case that, for example, the rare earth aluminummonoclinic (R₄Al₂O₉) is yttrium aluminum monoclinic (Y₄Al₂O₉), themaximum peak is generally a diffraction peak attributed to the (−122)plane of the crystalline lattice, however, not limited thereto. Thediffraction peak is normally detected at around 2θ=29.6°. In case that,for example, the rare earth oxide (R₂O₃) is cubic yttrium oxide (Y₂O₃),the maximum peak is generally a diffraction peak attributed to the (222)plane of the crystalline lattice, however, not limited thereto. Thediffraction peak is normally detected at around 2θ=29.2°.

The spraying material of the invention preferably has a specific surfacearea S of preferably at least 1 m²/g. The specific surface area S may bemeasured by BET method. The specific surface area S is more preferablyat least 1.1 m²/g. When a spraying material has a larger specificsurface area, heat of a frame readily reaches into the inside of theparticles during plasma spraying. Thus, when melted particles collidewith a substrate or a coating on a substrate and splats are formed, theresulting coating tends to be dense, and the splats are tightly bonded.An upper limit of the specific surface area S is preferably up to 3.5m²/g, more preferably up to 3 m²/g, however, not limited thereto. Aspraying material having a small specific surface area is possible toreduce fine particles that adhere to the surface portion of the formedcoating without entering to a thermal spray frame and cause particlecontamination, and fine particles that are vapored due to excessive heatinput through a thermal spray frame.

The spraying material of the invention preferably has a bulk density ρof up to 2 g/cm³. In the invention, an aerated bulk density may beadopted to the bulk density ρ. The bulk density ρ is more preferably upto 1.8 g/cm³. A spraying material having a low bulk density can form asprayed coating having a high hardness, since permeability of flame heatper unit particles is improved when the spraying material is used inplasma spraying. A lower limit of the bulk density ρ is preferably atleast 0.4 g/cm³, more preferably at least 0.5 g/cm³, however, notlimited thereto. When the spraying material has a high density, splatsare is easy to be formed from the spraying material to during plasmaspraying and a dense coating is easy to be formed. Further, it canreduce risk in degradation of properties of the resulting sprayedcoating, since the particle has less gas component included in void ofthe particle.

The spraying material of the invention preferably has a value S/ρ of 1to 4. The value S/ρ is obtained by dividing the specific surface area S(m²/g) by the bulk density ρ (g/cm³). A large value S/ρ means that thespecific surface area S is too large and the bulk density is too small.Therefore, when the value S/ρ is more than 4, particles that will causeparticle contamination, and particles that will easily form splatsformable a coarse coating may be increased. On the other hand, a smallvalue S/ρ means that the specific surface area S is too small and thebulk density is too large. Therefore, when the value S/ρ is less than 1,particles that will form a coarse coating due to increase of unmeltedportions, and particles that will lower hardness of the resultingcoating due to poor heat permeability may be increased. The value S/ρ ismore preferably at least 1.2, even more preferably at least 1.5, andmore preferably up to 3.8, even more preferably up to 3.5. When the rareearth oxide (R₂O₃) content and the aluminum oxide (Al₂O₃) content are,respectively, calculated from the basis of an rare earth (R) content andan aluminum content in the spraying material, the spraying material ofthe invention preferably has a composition corresponding to a relativerare earth oxide (R₂O₃) content of 75 to 99 wt % and a relative aluminumoxide (Al₂O₃) content of 1 to 25 wt % in the total content of the rareearth oxide (R₂O₃) and the aluminum oxide (Al₂O₃). The relative contentcalculated as the rare earth oxide (R₂O₃) content is more preferably atleast 80 wt %, even more preferably at least 85 wt %, and morepreferably up to 97 wt %, even more preferably up to 95 wt %. On theother hand, the relative content calculated as the aluminum oxide(Al₂O₃) is more preferably at least 3 wt %, even more preferably atleast 5 wt %, and more preferably up to 20 wt %, even more preferably upto 15 wt %.

In the spraying material of the invention, the total weight of mainoxide component (a composite oxide containing a rare earth and aluminum,and a rare earth oxide (in case of two species), or a composite oxidecontaining a rare earth and aluminum, a rare earth oxide, and analuminum oxide (in case of three species in which the aluminum oxide isfurther included) is assumed as the total weight of the relative contentof the rare earth oxide and the relative content of the aluminum oxide.Further, a weight of R₂O₃ as basic composition of a rare earth oxide anda weight of Al₂O₃ as basic composition of aluminum oxide that areconverted from a rare earth content and an aluminum content in thespraying material are assumed as the relative contents of the rare earthoxide and the aluminum oxide, respectively. A total content of oxidesother than the main oxide content is preferably up to 3 wt %, morepreferably up to 1 wt % in the spraying material. Most preferably, thespraying material is substantively free of the oxides except to the mainoxide content, i.e., the spraying material substantively consists of thetwo species or three species constituting the main oxide component,however not limited thereto. The contents of the rare earth and aluminumin the spraying material can be measured by, for example, ICP emissionoptical spectroscopy, fluorescence X-ray analysis, or the like. Sincerare earth and aluminum constituting the main oxide component can beselectively measured, fluorescence X-ray analysis is preferable.

The rare earth (R) in the spraying material of the invention includes atleast one element selected from the group consisting of yttrium (Y) andlanthanoids from lanthanum (La) to lutetium (Lu) that have atomicnumbers from 57 to 71, respectively. The rare earth (R) is preferablyselected from the group consisting of yttrium (Y), gadolinium (Gd),terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),ytterbium (Yb), and lutetium (Lu), more preferably selected from thegroup consisting of yttrium (Y), gadolinium (Gd), dysprosium (Dy),erbium (Er), and ytterbium (Yb). The rare earth (R) may be used assingle element or a combination of two or more elements.

The spraying material of the invention preferably has an averageparticle size D50 of up to 50 μm. The average particle size D50designates a cumulative 50% diameter (or median diameter) in a volumebasis particle size distribution. Particles of the spraying materialhaving a small particles size form splats having a small diameter whenthe particles collide with a substrate or a coating on a substrate,thereby a porosity of the formed sprayed coating becomes low, and crucksgenerated in the splats are controlled. The average particle diameterD50 is more preferably up to 45 μm, even more preferably up to 40 μm. Onthe other hand, the spraying material of the invention preferably has anaverage particle size D50 of at least 1 μm. Particles of the sprayingmaterial having a large particles size has a large momentum, thereby theparticles are easy to form splats when the particles collide with asubstrate or a coating on a substrate. The average particle diameter D50is more preferably at least 1.2 μm, even more preferably at least 1.5μm.

The particles of the spraying material of the invention may be used as aspraying material in slurry form (a spraying slurry for thermalspraying) that includes particles of the spraying material dispersed ina dispersion medium. A content of the spraying material particles in thewhole of the spraying slurry is preferably up to 70 wt %. If the contentof the thermal spraying material exceeds 70 wt %, the slurry may becomeblocked in a supply device during thermal spraying, thus a sprayedcoating cannot be formed. When the content of the spraying materialparticles in the spraying slurry is low, particles actively move in flowof the slurry, and dispersibility is improved. Further, when the contentof the spraying material particles is low, flowability of the slurry isimproved, thereby it is preferable for slurry supply. The content ofspraying material particles is more preferably up to 65 wt %, even morepreferably up to 60 wt %, most preferably up to 52 wt %. When a highflowability is needed, a lower content of the thermal spraying materialcan be adopted, and the content in the case is preferably up to 45 wt %,more preferably up to 40 wt %, even more preferably up to 35 wt %. Onthe other hand, the content of the spraying material particles in thewhole of the spraying slurry is preferably at least 10 wt %. When thecontent of the spraying material particles in the spraying slurry ishigh, adhesive efficiency of a sprayed coating formed by thermalspraying of the slurry is improved, thereby it is possible to reduceconsumed amount of slurry or to improve a thermal spraying yield.Further, when the content of the spraying material particles is high, aspraying time can be shortened. The content of spraying materialparticles is more preferably at least 15 wt %, even more preferably atleast 20 wt %.

The spraying slurry may include particles other than the sprayingmaterial of the invention, for example, particles of a rare earthcompound not including the composite oxide containing a rare earth andaluminum, in case of a small amount which does not impact to the effectsof the present invention. The particles other than the spraying materialof the invention is preferably up to 10 wt %, more preferably up to 5 wt%, even more preferably 3 wt % to the spraying material of the inventionincluded in the spraying slurry. Most preferably, the spraying slurry issubstantively free of the particles other than the spraying material ofthe invention. Examples of the rare earth compound constituting theparticles other than the spraying material include a rare earth oxide, arare earth fluoride, a rare earth oxyfluoride, a rare earth hydroxide, arare earth carbonate, and so on.

When the spraying material of the invention is dispersed with adispersion medium to form a spraying slurry, one or more kinds ofdispersion mediums selected from aqueous dispersion mediums arepreferably used. For the aqueous dispersion medium, water alone or amixture of water and an organic solvent may be used. Examples of theorganic medium include, for example, an alcohol, an ether, an ester, aketone, and so on, however not limited thereto. In particular, morepreferable examples include a monohydric or dihydric alcohol having 2 to6 carbon atoms, an ether having 3 to 8 carbon atoms such as ethylcellosolve, a glycol ether having 4 to 8 carbon atoms such asdimethyldiglycol (DMDG), a glycol ester having 4 to 8 carbon atoms suchas ethyl cellosolve acetate and butyl cellosolve acetate, and a cyclicketone having 6 to 9 carbon atoms such as isophorone. A water-solubleorganic solvent which can be mixed with water is more suitable for theorganic solvent. Most preferable dispersion medium is water or a mixtureof water and an alcohol. When the mixture of water and an organicsolvent is used, as a mixing ratio of the water and organic solvent, acontent of the water is preferably at least 50 wt %, more preferably atleast 70 wt %, and preferably less than 100 wt %, more preferably up to99 wt %, and a content of the organic solvent is preferably more than 0wt %, more preferably at least 1 wt %, and preferably up to 50 wt %,more preferably up to 30 wt %.

When the spraying material of the invention is dispersed with adispersion medium to form a spraying slurry, the spraying slurrypreferably includes a dispersing agent to prevent agglomeration ofparticles effectively. A content of the dispersing agent in the whole ofthe spraying slurry is preferably up to 3 wt %. As the dispersing agent,a cationic dispersing agent, an anionic dispersing agent, a nonionicdispersing agent, and the like are used, however, not limited thereto.Examples of the cationic dispersing agent include apolyalkyleneimine-based cationic dispersing agent, apolyalkylenepolyamine-based cationic dispersing agent, a quaternaryammonium-based cationic dispersing agent, and an alkylamine-basedcationic dispersing agent. Examples of the anionic dispersing agentinclude a polycarboxylic acid-based anionic dispersing agent, apolyacrylic acid-based anionic dispersing agent, and a polysulfonicacid-based anionic dispersing agent. Examples of the nonionic dispersingagent include a polyvinyl alcohol-based nonionic dispersing agent and apolyacrylamide-based nonionic dispersing agent. A content of thedispersing agent in the spraying slurry is more preferably up to 2 wt %,even more preferably up to 1 wt %.

The spraying slurry preferably has a viscosity of less than 15 mPa·s. Alow viscosity provides active movement of particles in the slurry andimprovement of flowability of the slurry. The viscosity of the slurry ismore preferably up to 10 mPa·s, even more preferably up to 7 mPa·s. Alower limit of the viscosity is preferably at least 1 mPa·s, morepreferably at least 1.5 mPa·s, even more preferably at least 2 mPa·s,however not limited thereto.

The spraying slurry preferably has a particle sedimentation rate of atleast 50 μm/s. A high sedimentation rate means that particles are mobilein the slurry with less effect of resistance from surround. A highsedimentation rate results in improvement of flowability of particlesincluded in the slurry. The sedimentation rate is more preferably atleast 55 μm/s, even more preferably at least 60 μm/s.

The spraying material of the invention may be prepared by, for example,a method including steps of:

(A) forming a slurry by dispersing an aluminum oxide in an aqueoussolution of a rare earth salt;

(B) crystalizing a precursor containing the rare earth and aluminum, asa precipitate, by adding a precipitant to the slurry;

(C) collecting the precipitate by a solid-liquid separation; and

(D) firing the precursor containing the rare earth and aluminum under anoxygen-containing gas atmosphere.

In this method, a precursor is preliminarily provided for preparing thespraying material. In the step (A), a slurry is formed by dispersing analuminum oxide in an aqueous solution of a rare earth salt. At thistime, with respect to the rare earth salt and aluminum oxide, a ratio ofthe rare earth salt and aluminum oxide is preferably adjusted such thatthe ratio of the rare earth and aluminum contained in the resultingspraying material corresponds to a ratio within the ranges of theabove-mentioned relative content of the rare earth oxide (R₂O₃) and therelative content of the aluminum oxide (Al₂O₃) in the spraying material.Examples of the rare earth salt include a nitrate, a chloride, and soon.

Next, in the step (B), a precipitant is added to the slurry. Theprecipitant is added into the aqueous solution of a rare earth salt inwhich the aluminum oxide is uniformly dispersed. Examples of theprecipitant include oxalic acid, urea, ammonium carbonate, ammoniumhydrogencarbonate, and so on. The amount of the precipitant added ispreferably 5 to 20 times of the molar amount of the rare earth (R). Whenthe precipitant is added into the slurry, the rare earth salt reactswith the precipitant, and the precursor containing the rare earth andaluminum is crystallized as a precipitate. The reaction temperature isusually 70 to 100° C., and the reaction time is usually 2 to 12 hours.

Next, in the step (C), the precipitate which is the precursor containingthe rare earth and aluminum is separated by a solid-liquid separationsuch as a filtration with optional washing, and the precursor containingthe rare earth and aluminum is collected as hydrous solids. If needed,the collected precipitate may be pre-fired under an oxygen-containinggas atmosphere such as air atmosphere. The pre-firing is performed, forexample, at a temperature of 600 to 1,000° C., and for 1 to 8 hours.Notably, the pre-firing is applied such that the reaction from theprecursor to the spraying material of the present invention is notcompleted. After the pre-firing, the precipitate may be crushed by acrusher such as a hammer mill, if needed.

Next, in the step (D), the precursor containing the rare earth andaluminum is fired under an oxygen-containing gas atmosphere such as airatmosphere. Herein, before firing of the precursor, granule may beformed from the particles of the precursor by granulation. Thegranulation is a method of forming particles having a large particlesize by collecting and integrating particles having a small particlesize, and generally, particles having voids between the integratedparticles having a small particle size are obtained. A firingtemperature is preferably 900 to 1,700° C. The firing temperature ismore preferably at least 1,000° C., even more preferably at least 1,100°C., most preferably at least 1,200° C. A firing time is generally, 2 to6 hours.

When a spraying material having an average particle diameter D50 of 1 to10 μm is prepared, the particles tend to agglomerate strongly afterfiring. Thus, if needed, the obtained spraying material after firing maybe pulverized by, for example, a ball mill or a jet mill, and may besieved.

When a spraying material having an average particle diameter D50 of 10to 50 μm is prepared, granulation is effective for preparing thespraying material. In this case, the preparing method may include stepsof, for example, firing the obtained precursor at 900 to 1,700° C.;optionally pulverizing by, for example, a ball mill or a jet mill;optionally sieving; preparing a slurry of the obtained powder;granulating by a spray dryer; and further firing at 1,100 to 1,700° C.In this case, the resulting spraying material may be sieved, if needed.

According to the invention, a sprayed coating (a surface layer coating)including a composite oxide containing a rare earth and aluminum whichis suitably applied to parts or members for semiconductor manufacturingapparatus can be formed directly or via an underlaying coating (a lowerlayer coating) on a substrate, for example, by using the sprayingmaterial of the invention. Further, a sprayed member including thesprayed coating (surface layer coating) which is formed directly on asubstrate or via the underlaying coating (lower layer coating) on asubstrate can be manufactured.

Examples of a material of the substrate include an inorganic compound(ceramics) such as stainless steel, aluminum, nickel, chromium, zinc andalloys thereof, alumina, zirconia, aluminum nitride, silicon nitride,silicon carbide and quartz glass, and carbon, and so on, however notlimited thereto. A suitable material is selected in accordance with theuse (for example, for a semiconductor manufacturing apparatus) of thesprayed member. For example, in the case of an aluminum metal oraluminum alloy substrate, a substrate applied with alumite treatmenthaving acid resistance is preferable. A shape of the substrate may be,for example, a flat plate shape or a cylinder shape, however, notlimited thereto.

When a sprayed coating is formed on a substrate, for example, it ispreferable that the surface of the substrate on which the sprayedcoating will be formed is degreased with acetone and subjected to asurface roughening treatment using an abrasive such as corundum toincrease a surface roughness Ra. By the surface roughening treatment ofthe substrate, it is possible to effectively suppress peeling of thecoating caused by difference in the thermal expansion coefficientbetween the sprayed coating and the substrate. The grade of the surfaceroughening treatment may be appropriately adjusted in accordance withthe material of the substrate.

By forming preliminary a lower layer coating on a substrate before asprayed coating is formed, the sprayed coating can be formed via anunderlaying coating. The underlaying coating may form to 50 to 300 μmthick. When the sprayed coating is formed on the lower layer coating,preferably in contact with the lower layer coating, the underlayingcoating and the sprayed coating can be formed as the lower layer coatingand the surface layer coating, respectively, thereby the coating isformed as a coating having a multilayer structure.

Examples of a material of the underlaying coating include a rare earthoxide, a rare earth fluoride, a rare earth oxyfluoride, and the like. Asthe rare earth constituting the material of the underlaying coating, thesame elements exemplified as the rare earth (R) in the spraying materialcan be exemplified, and yttrium (Y) is preferable. The underlayingcoating can be formed by thermal spraying such as atmospheric plasmaspraying or suspension plasma spraying, under normal pressure.

The underlaying coating has a porosity of preferably up to 5%, morepreferably up to 4%, even more preferably up to 3%. A lower limit of theporosity is normally at least 0.1%, however not limited thereto. Theunderlaying coating has a surface roughness Ra of preferably up to 10μm, more preferably up to 6 μm. A low surface roughness Ra ispreferable, however, a lower limit of the surface roughness Ra isnormally at least 0.1 μm. When the sprayed coating as the surface layercoating is formed on the lower layer coating having a low Ra, preferablyin contact with the lower layer coating, it is preferable since thesurface roughness Ra of the surface layer coating can also be reduced.

The lower layer coating having such a low porosity and/or a low surfaceroughness Ra may be formed by, for example, a method including steps ofproviding, as a source material, a single particle powder or agranulated spray powder having an average particle size D50 of at least0.5 μm, preferably at least 1 μm, and up to 50 μm, preferably up to 30μm, and thermal spraying with melting particles sufficiently by plasmaspraying or explosion spraying, however, not limited thereto. The methodcan form a dense lower layer coating having a low porosity and/or a lowsurface roughness Ra. It is noted that “single particle powder” is apowder composed of particles that are spherical particles, angularparticles or grinded particles, and have a solidly packed interior. Whenthe single particle powder is used, even if the single particle powderhas a smaller particle size than the granulated spray powder, since thesingle particle powder consists of particles having a solidly packedinterior, splat diameter is small. Thus, it can form a lower layercoating in which cracks are suppressed.

The surface roughness Ra of the lower layer coating can be reduced by asurface machining such as a mechanical polishing (surface grinding,inner cylinder processing, mirror surface processing, etc.), blastingusing fine beads, hand polishing using a diamond pad, and the like.

A thermal spraying method of the invention to form a sprayed coating (asurface layer coating) by using a spraying material is preferably aplasma spraying, however, not limited thereto. The plasma spraying maybe atmospheric plasma spraying or suspension plasma spraying.

Plasma gases used to form plasma in atmospheric plasma spraying mayinclude argon gas alone, nitrogen gas alone, and a mixed gas consistingof at least two kinds of gases selected from the group consisting ofargon gas, hydrogen gas, helium gas and nitrogen gas, however, notlimited thereto. A spraying distance in atmospheric plasma spraying ispreferably up to 150 mm. A shorter spraying distance imparts improvementof adhesion efficiency, increase of hardness, and reduction of porosity,of the sprayed coating. The spraying distance is more preferably up to140 mm, even more preferably up to 130 mm. A lower limit of the sprayingdistance is preferably at least 50 mm, more preferably at least 60 mm,even more preferably 70 mm, however not limited thereto.

Plasma gases used to form plasma in suspension plasma spraying mayinclude a mixed gas consisting of at least two kinds of gases selectedfrom the group consisting of argon gas, hydrogen gas, helium gas andnitrogen gas, preferably a mixed gas of three kinds consisting of argongas, hydrogen gas and nitrogen gas, more preferably a mixed gas of fourkinds consisting of argon gas, hydrogen gas, helium gas and nitrogengas, however, not limited thereto. A spraying distance in suspensionplasma spraying is preferably up to 100 mm. A shorter spraying distanceimparts improvement of adhesion efficiency, increase of hardness, andreduction of porosity, of the sprayed coating. The spraying distance ismore preferably up to 90 mm, even more preferably up to 80 mm. A lowerlimit of the spraying distance is preferably at least 50 mm, morepreferably at least 55 mm, even more preferably 60 mm, however notlimited thereto.

When a sprayed coating is formed on a substrate or on a coating (a lowerlayer coating) formed on a substrate, the thermal spraying is preferablyconducted with cooling the substrate, and/or the coating (lower layercoating) formed on the substrate, and further with cooling the formedsprayed coating (surface layer coating). The cooling may be, forexample, air cooling or water cooling.

Particularly, a temperature of the substrate or the substrate and thecoating formed on the substrate is preferably at least 100° C. duringthermal spraying. When a higher temperature is applied, bonding betweenthe substrate and the resulting sprayed coating, or the coating (lowerlayer coating) formed on the substrate and the resulting sprayed coatingbecomes strong, and a dense sprayed coating can be formed. Further, whenthe temperature is higher, quenching stress generates, thereby ahardness of the resulting sprayed coating is improved. During thermalspraying, the temperature of the substrate, or the substrate and thecoating formed on the substrate is more preferably at least 130° C.,even more preferably at least 150° C.

On the other hand, a temperature of the substrate or the substrate andthe coating formed on the substrate is preferably up to 300° C. duringthermal spraying. When a lower temperature is applied, damage ordeformation of the substrate or the substrate and the coating formed onthe substrate caused by heat can be prevented, thereby peeling betweenthe substrate and the resulting sprayed coating, or the coating (lowerlayer coating) formed on the substrate and the resulting sprayed coatingcan be prevented. During thermal spraying, the temperature of thesubstrate, or the substrate and the coating formed on the substrate ismore preferably up to 270° C., even more preferably up to 250° C. Thetemperature can be accomplished by controlling cooling ability.

Other spraying conditions such as a supply rate of the spray material(spraying slurry), amounts of gas supply, and an applied power (currentvalue, and voltage value) in plasma spraying are not particular limited,commonly known conditions can be applied. They may be adjustedappropriate in accordance with the substrate, the spraying material, theapplication of the resulting sprayed member, and the like.

In particular, as described above, when the sprayed coating is formeddirectly on the substrate, it is possible to form a harder and densesprayed coating that is hard to peel by increasing the surface roughnessRa of the substrate surface on which the sprayed coating is formed, andfurther applying the above-mentioned temperature. In such a case, thesurface roughness Ra of the formed sprayed coating tends to be high.Thus, when the surface roughness Ra is decreased by mechanical polishing(surface grinding, inner cylinder processing, mirror surface processing,etc.), blasting using fine beads, hand polishing using a diamond pad,and the like, it is possible to form a lubricative sprayed coating thatis hard to peel, and is a harder and dense coating having a low surfaceroughness Ra.

The sprayed coating of the invention is suitable for use as parts ormembers in a plasma etching apparatus which is employed in asemiconductor manufacturing process. The sprayed coating of theinvention preferably includes a rare earth (R), aluminum and oxygen, anda crystalline phase of a composite oxide containing the rare earth (R)and aluminum. The sprayed coating of the invention has superior plasmaetching resistance (corrosion resistance) with reduced amount ofparticles generated by a corrosive halogen-based gas plasma.

The sprayed coating of the invention preferably includes, as thecrystalline phase of a composite oxide containing the rare earth andaluminum, a crystalline phase of a composite oxide that includes acrystalline phase having a rare earth-rich composition compared to thestoichiometric composition of rare earth aluminum monoclinic (R₄Al₂O₉),and having a structure such that Al atom sites in the rare earthaluminum monoclinic (R₄Al₂O₉) are partially substituted with the rareearth (R) atoms.

The sprayed coating including the crystalline phase of a composite oxidethat includes a crystalline phase having a rare earth-rich compositioncompared to the stoichiometric composition of rare earth aluminummonoclinic (R₄Al₂O₉) can be formed, for example, by thermal spraying,particularly, by plasma spraying, of the spraying material of theinvention. The crystalline phase of a composite oxide that includes acrystalline phase having a rare earth-rich composition compared to thestoichiometric composition of rare earth aluminum monoclinic (R₄Al₂O₉)can be confirmed by an XRD diffraction peak detected at a diffractionangle that is 0.05 to 0.5° (in difference) lower than the diffractionangle attributed to the maximum XRD diffraction peak of the rare earthaluminum monoclinic (R₄Al₂O₉), particularly, the diffraction angleattributed to the maximum XRD diffraction peak of the rare earthaluminum monoclinic (R₄Al₂O₉) in the spraying material used for formingthe sprayed coating. The difference is preferably at least 0.1°, andpreferably up to 0.3°.

In case that, for example, the rare earth aluminum monoclinic (R₄Al₂O₉)is yttrium aluminum monoclinic (Y₄Al₂O₉), the maximum peak is generallya diffraction peak attributed to the (−122) plane of the crystallinelattice, however, not limited thereto. The diffraction peak is normallydetected at around 2θ=29.6°. Further, a peak of the crystalline phasehaving a rare earth-rich composition compared to the stoichiometriccomposition of rare earth aluminum monoclinic (R₄Al₂O₉) is normallydetected also at a part or the whole of diffraction angles other thanthe maximum peak, and at a diffraction angle that is lower than the peakattributed to the XRD diffraction peak of the rare earth aluminummonoclinic (R₄Al₂O₉).

In the crystalline phase of the composition oxide having a rareearth-rich composition compared to the stoichiometric composition ofrare earth aluminum monoclinic (R₄Al₂O₉), a part of Al sites (Al³+ ions)in R₄Al₂O₉ is replaced with R sites (R³⁺ ions) by isomorphoussubstitution, and the lattice spacing d is expanded. Diffraction peaksof the composite oxide having a rare earth-rich composition compared tothe stoichiometric composition of rare earth aluminum monoclinic(R₄Al₂O₉) depend to Bragg's condition of diffraction: 2d sin θ=nλ,wherein d is a lattice spacing, θ is a glancing angle, n is a positiveintegral number, and λ is a wavelength of X-ray. Thus, it is consideredthat the peaks appear at a lower angle than the diffraction angle of thediffraction peak attributed to the rare earth aluminum monoclinic(R₄Al₂O₉) because the glancing angle θ of X-ray is decreased. In casethat, for example, the rare earth aluminum monoclinic (R₄Al₂O₉) isyttrium aluminum monoclinic (Y₄Al₂O₉), a part of Al³⁺ ions (ion radiusof 0.533 Å in six-coordination) in Y₄Al₂O₉ is replaced with R³⁺ ions(ion radius of 0.900 Å in six-coordination) that have larger ion radiusby isomorphous substitution, then, the lattice spacing d is expanded.

Diffraction peaks of the composite oxide having a rare earth-richcomposition compared to the stoichiometric composition of rare earthaluminum monoclinic (R₄Al₂O₉) is not listed in X-ray diffractiondatabases such as the JCPDS. However, detection of the peak sifting tolower angle than the diffraction angle of the diffraction peakattributed to the rare earth aluminum monoclinic (R₄Al₂O₉) means thatthe crystalline phase having a rare earth-rich composition compared tothe stoichiometric composition of rare earth aluminum monoclinic(R₄Al₂O₉) exists.

In view point of corrosion resistance, rare earth oxide (R₂O₃) issuperior to the rare earth aluminum monoclinic (R₄Al₂O₉). Thus, it canbe said that the composite oxide having a rare earth-rich compositioncompared to the stoichiometric composition of rare earth aluminummonoclinic (R₄Al₂O₉) has an advantage in corrosion resistance. A sprayedcoating including a mixed phase of a crystalline phase of the rare earthaluminum monoclinic (R₄Al₂O₉) and a crystalline phase of rare earthoxide (R₂O₃) have not been ever obtained by plasma spraying.Particularly, a sprayed coating including the crystalline phase of thecomposite oxide having a rare earth-rich composition compared to thestoichiometric composition of rare earth aluminum monoclinic (R₄Al₂O₉)has not been known. The sprayed coating of the invention that includesthe crystalline phase of the composite oxide having a rare earth-richcomposition compared to the stoichiometric composition of rare earthaluminum monoclinic (R₄Al₂O₉) has superior plasma etching resistance(corrosion resistance) with extremely reduced amount of particlesgenerated by a corrosive halogen-based gas plasma.

The sprayed coating of the invention may include a crystalline phase ofa rare earth oxide (R₂O₃). Inclusion of the rare earth oxide isadvantageous in that the corrosion resistance of the thermal spraycoating is improved.

The sprayed coating of the invention may include at least onecrystalline phase selected from the group consisting of a rare earthaluminum monoclinic (R₄Al₂O₉), a rare earth aluminum perovskite (RAlO₃),and a rare earth aluminum garnet (R₃Al₅O₁₂). Inclusion of R₄Al₂O₉, RAlO₃or R₃Al₅O₁₂ is advantageous in that an amount of particles generatedfrom the sprayed coating is reduced.

When the rare earth oxide (R₂O₃) content and the aluminum oxide (Al₂O₃)content are, respectively, calculated from the basis of an rare earth(R) content and an aluminum content in the sprayed coating, the sprayedcoating of the invention preferably has a composition corresponding to arelative rare earth oxide (R₂O₃) content of 75 to 99 wt % and a relativealuminum oxide (Al₂O₃) content of 1 to 25 wt % in the total content ofthe rare earth oxide (R₂O₃) and the aluminum oxide (Al₂O₃). The relativecontent calculated as the rare earth oxide (R₂O₃) content is morepreferably at least 80 wt %, even more preferably at least 85 wt %, andmore preferably up to 97 wt %, even more preferably up to 95 wt %. Onthe other hand, the relative content calculated as the aluminum oxide(Al₂O₃) is more preferably at least 3 wt %, even more preferably atleast 5 wt %, and more preferably up to 20 wt %, even more preferably upto 15 wt %.

In the sprayed coating of the invention, the total weight of main oxidecomponent (a composite oxide containing rare earth and aluminum, a rareearth oxide, and an aluminum oxide) is assumed as the total weight ofthe relative content of the rare earth oxide and the relative content ofthe aluminum oxide. Further, a weight of R₂O₃ as basic composition of arare earth oxide and a weight of Al₂O₃ as basic composition of aluminumoxide that are converted from a rare earth content and an aluminumcontent in the sprayed coating are assumed as the relative contents ofthe rare earth oxide and the aluminum oxide, respectively. Preferably,the sprayed coating is substantively free of the oxides except to themain oxide content, i.e., the sprayed coating substantively consists ofone or more species constituting the main oxide component, however notlimited thereto. The contents of the rare earth and aluminum in thesprayed coating can be measured by, for example, ICP emission opticalspectroscopy, fluorescence X-ray analysis, or the like. Since rare earthand aluminum constituting the main oxide component can be selectivelymeasured, fluorescence X-ray analysis is preferable.

The rare earth (R) in the sprayed coating of the invention includes atleast one element selected from the group consisting of yttrium (Y) andlanthanoids from lanthanum (La) to lutetium (Lu) that have atomicnumbers from 57 to 71, respectively. The rare earth (R) is preferablyselected from the group consisting of yttrium (Y), gadolinium (Gd),terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),ytterbium (Yb), and lutetium (Lu), more preferably selected from thegroup consisting of yttrium (Y), gadolinium (Gd), dysprosium (Dy),erbium (Er), and ytterbium (Yb). The rare earth (R) may be used assingle element or a combination of two or more elements.

The sprayed coating has a surface roughness Ra of up to preferably up to8 μm. When the sprayed coating has a surface roughness Ra of up to 8 μm,it is advantageous in that generation of particles caused by ahalogen-based gas plasma can be further suppressed. The surfaceroughness Ra is more preferably up to 7 μm, even more preferably up to 6μm. On the other hand, a low surface roughness Ra is preferable,however, a lower limit of the surface roughness Ra is normally at least0.1 μm. When the surface roughness Ra is at least 0.1 μm, it is hard todamage the sprayed coating by excessively machining during adjustment ofcoating thickness, and it is hard to cause particle separation.

The sprayed coating of the invention preferably has a thickness of atleast 10 μm. when the thickness is at least 10 μm, corrosion resistanceto a halogen-based gas plasma is more effectively exerted. The thicknessis more preferably at least 30 μm, even more preferably at least 50 μm.On the other hand, an upper limit of the thickness is preferably up to500 μm. When the thickness of the sprayed coating is up to 500 μm, thesprayed coating is hard to be peeled from the substrate or the coating(lower layer coating) formed on the substrate. The upper limit of thethickness is more preferably up to 400 μm, even more preferably up to300 μm.

The sprayed coating of the invention preferably has a Vickers hardnessHV 0.3 of at least 600. When the Vickers hardness HV 0.3 is at least600, it is hard to be etched the surface of coating by plasma etching ofa halogen-based gas plasma, and corrosion resistivity becomes higher.The Vickers hardness HV 0.3 is more preferably at least 630, even morepreferably at least 650. On the other hand, a high Vickers hardness HV0.3 is preferable, however, an upper limit of the Vickers hardness HV0.3 is normally up to 1,000. When the Vickers hardness HV 0.3 is up to1,000, the sprayed coating is hard to be peeled from the substrate orthe coating (lower layer coating) formed on the substrate.

The sprayed coating of the invention preferably has a porosity of up to5%. When the porosity is up to 5%, it is advantageous in that generationof particles caused by a halogen-based gas plasma can be furthersuppressed. Further, it is advantageous in that corrosion resistivitytends to be improved. The porosity is more preferably up to 4%, evenmore preferably up to 3%. Notably, a lower limit of the porosity isnormally at least 0.1%. however, not limited thereto.

EXAMPLES

Examples of the invention are given below by way of illustration and notby way of limitation.

Example 1

Yttrium nitrate (Y(NO₃)₃) and aluminum oxide (Al₂O₃) were provided inthe ratio indicated in Table 1 so that the relative contents of theyttrium oxide (Y₂O₃) and the relative content of the aluminum oxide(Al₂O₃) in the total content of the yttrium oxide (Y₂O₃) and thealuminum oxide (Al₂O₃) match to the ratio in the resulting sprayingmaterial. Then, a slurry was prepared by dispersing a powder of aluminumoxide (Al₂O₃) having an average particle size D50 of 0.5 μm to 0.01mol/L of yttrium nitrate aqueous solution. Next, urea was added into thesolution in the corresponding amount of 10 mol of urea per 1 mol ofyttrium nitrate, the solution was stirred, and a precipitate wascrystalized. Then, the obtained precipitate was collected as a precursorcontaining rare earth (yttrium) and aluminum by solid-liquid separation.

Next, the obtained precipitate (precursor) was dispersed in water toprepare a slurry with adding carboxymethyl cellulose as a binder. Theobtained slurry was granulated by using a spray drier, and the obtainedgranulated particles were fired at 1,600° C. for 2 hours in airatmosphere to obtain a spraying material.

Crystalline phases of the obtained spraying material were identified byX-ray diffraction (XRD), constituent crystals were analyzed, and themaximum peak was specified. Then, an intensity ratio I(R)/I(RAL) of anintegral intensity I(R) of the maximum diffraction peak attributed to arare earth oxide (R₂O₃) to an integral intensity I(RAL) of the maximumdiffraction peak attributed to a rare earth aluminum monoclinic(R₄Al₂O₉) was calculated. X-ray diffraction (XRD) was measured by anX-ray diffraction analyzer, X'Pert PRO/MPD, manufactured by MalvernPanalytical Ltd.), and by an analysis software, HighScore Plus,manufactured by Malvern Panalytical Ltd.), crystalline phases wereidentified and the integral intensities ware calculated. The measurementconditions were as follows: characteristic X-ray: Cu-Kα (tube voltage:45 kV, tube current: 40 mA), scan range 2θ: 5 to 70°, step size:0.0167113°, time-per-step: 13.970 seconds, scan speed: 0.151921°/sec. ABET specific surface area S and a bulk density ρ were measured, and S/ρwas calculated. From the results of quantification of yttrium andaluminum by X-ray fluorescence analysis, the ratio of yttrium andaluminum was calculated as the relative contents of the yttrium oxide(Y₂O₃) and the relative content of the aluminum oxide (Al₂O₃) in thetotal of both contents. Further, a particle size distribution (anaverage particle diameter D50) was measured. The results were shown inTable 1. Notably, a diffraction angle (2θ(RAL)) of the maximum peakattributed to the rare earth aluminum monoclinic (R₄Al₂O₉) is shown inTable 3. Detail of respective measurement or analysis is describedlater.

Example 2

A precursor was obtained by the same method in Example 1, and theobtained precursor was fired at 1,600° C. for 2 hours in air atmosphere,and pulverized by a jet mill to obtain a spraying material. The obtainedspraying material was measured or analyzed by the same methods inExample 1. The results are shown in Tables 1 and 3. Further, the XRDprofile is shown in FIG. 1.

Further, the obtained spraying material and a dispersing agent weremixed with a dispersion medium, and the spraying material was dispersedin the dispersion medium to obtain a spraying material in slurry form.The slurry concentration, the dispersion medium used, the dispersingagent used and the concentration of the dispersing agent in the slurryare shown in Table 2. Further, a viscosity of the obtained slurry wasmeasured. The result is shown in Table 2. Notably, detailed measurementof the viscosity is described later.

Example 3

A spraying material was obtained by the same method in Example 2 exceptthat the firing temperature and time for the precursor were set to1,300° C. and 4 hours, respectively. The obtained spraying material wasmeasured or analyzed by the same methods in Example 1. The results areshown in Tables 1 and 3. Further, a spraying material in slurry form wasobtained by the same method in Example 2, and a viscosity was measured.The slurry concentration, the dispersion medium used, the dispersingagent used, the concentration of the dispersing agent in the slurry, andthe viscosity are shown in Table 2.

Example 4

A precursor was obtained by the same method in Example 1 except thatyttrium (Y) was changed to gadolinium (Gd) (yttrium nitrate: Y(NO₃)₃, asa source material, was changed to gadolinium nitrate: Gd(NO₃)₃), and theobtained precursor was fired at 1,200° C. for 2 hours in air atmosphere,and pulverized by a jet mill to obtain a spraying material. The obtainedspraying material was measured or analyzed by the same methods inExample 1. The results are shown in Tables 1 and 3. Further, a sprayingmaterial in slurry form was obtained by the same method in Example 2,and a viscosity was measured. The slurry concentration, the dispersionmedium used, the dispersing agent used, the concentration of thedispersing agent in the slurry, and the viscosity are shown in Table 2.

Example 5

A precursor was obtained by the same method in Example 1 except thatyttrium (Y) was changed to ytterbium (Yb) (yttrium nitrate: Y(NO₃)₃, asa source material, was changed to ytterbium nitrate: Yb(NO₃)₃), and theobtained precursor was fired at 1,500° C. for 2 hours in air atmosphere,and pulverized by a jet mill to obtain a spraying material. The obtainedspraying material was measured or analyzed by the same methods inExample 1. The results are shown in Tables 1 and 3. Further, a sprayingmaterial in slurry form was obtained by the same method in Example 2,and a viscosity was measured. The slurry concentration, the dispersionmedium used, the dispersing agent used, the concentration of thedispersing agent in the slurry, and the viscosity are shown in Table 2.

Example 6

A spraying material obtained by the same method in Example 2 wasmeasured or analyzed by the same methods in Example 1. The results areshown in Tables 1 and 3. Further, a spraying material in slurry form wasobtained by the same method in Example 2, and a viscosity was measured.The slurry concentration, the dispersion medium used and the viscosityare shown in Table 2.

Comparative Example 1

Yttrium oxide (Y₂O₃) powder having an average particle size D50 of 1.2μm was dispersed in water with adding carboxymethyl cellulose as adispersing agent to prepare a slurry. The obtained slurry was granulatedby s spray dryer to form granulated particles, and the obtainedgranulated particles were fired at 1,600° C. for 2 hours in airatmosphere to obtain a spraying material. The obtained spraying materialwas measured or analyzed by the same methods in Example 1. The resultsare shown in Table 1.

Comparative Example 2

Yttrium oxide (Y₂O₃) and aluminum oxide (Al₂O₃) were provided in theratio indicated in Table 1 so that the relative contents of the yttriumoxide (Y₂O₃) and the relative content of the aluminum oxide (Al₂O₃) inthe total content of the yttrium oxide (Y₂O₃) and the aluminum oxide(Al₂O₃) match to the ratio in the resulting spraying material. Then, aslurry was prepared by dispersing them in water with addingcarboxymethyl cellulose as a dispersing agent. The obtained slurry wasmixed and pulverized in a pot made of aluminum oxide of a ball mill byballs made of aluminum oxide for 24 hours. Next, the obtained slurryafter mixing and pulverizing was granulated by s spray dryer to formgranulated particles, and the obtained granulated particles were firedat 1,400° C. for 2 hours in air atmosphere to obtain a sprayingmaterial. The obtained spraying material was measured or analyzed by thesame methods in Example 1. The results are shown in Table 1.

Comparative Example 3

Yttrium oxide (Y₂O₃) was fired at 1,600° C. for 2 hours in airatmosphere, pulverized by a jet mill, and sieved to obtain a sprayingmaterial. The obtained spraying material was measured or analyzed by thesame methods in Example 1. The results are shown in Table 1. Further, aspraying material in slurry form was obtained by the same method inExample 2, and a viscosity was measured. The slurry concentration, thedispersion medium used, the dispersing agent used, the concentration ofthe dispersing agent in the slurry, and the viscosity are shown in Table2.

TABLE 1 Example Comparative Example 1 2 3 4 5 6 1 2 3 Crystalline Y₂O₃Gd₂O₃ Yb₂O₃ Y₂O₃ Y₂O₃ Y₃Al₅O₁₂ Y₂O₃ phase by XRD Y₄Al₂O₉ Gd₄Al₂O₉Yb₄Al₂O₉ Y₄Al₂O₉ I(R)/I(RAL) 2 2.4 1.2 2.3 1.1 2.4 — — — Specificsurface 2.5 1.2 1.7 1.1 2 1.2 0.6 3.8 0.8 area S (m²/g) Bulk density ρ1.38 0.75 0.58 0.9 1.1 0.75 2.04 0.8 0.92 (g/cm³) S/ρ 1.8 1.6 2.9 1.21.8 1.6 0.3 4.8 0.9 Rare earth oxide 89.7 91.9 86.9 93.5 92.5 91.9 10057.5 100 (wt %) Aluminum 10.3 8.1 13.1 6.5 7.5 8.1 0 42.5 0 oxide (wt %)D50 (μm) 38.1 2.9 2.1 3.8 1.8 2.9 30.4 40 3.2

TABLE 2 Example Comparative Example 2 3 4 5 6 3 Concentration 30  35 2025 70 30 of slurry (wt %) Dispersion water water 80 wt % of water +water 70 wt % of water + water medium 20 wt % of ethanol 30 wt % of2-propanol Dispersing Polyalkylene- Polyvinyl Polyalkylene- nilPolyalkylene- agent (wt %) imine-based alcohol-based imine-basedimine-based 1 0.05 0.5 0.05  3 Viscosity of 3 4 7 4 10 15 slurry (mPa ·s)

Examples 7 to 12 and Comparative Examples 4 to 6

A prayed coating was obtained by forming a sprayed coating directly orvia an underlaying coating on a substrate by plasma spraying with usingthe spraying material of Example 1 to 5 or Comparative Example 1 to 3.The substrate was made of the material shown in Table 3, and the surfaceof the substrate was subjected to a surface roughening treatment byblast polishing using a corundum abrasive having a grain size shown inTable 3. The sprayed coating, as a surface layer coating shown in Table3 was formed by atmospheric plasma spraying (APS) with using a sprayingmaterial in powder form in Example 7 and Comparative Examples 4 and 5,and formed by suspension plasma spraying (SPS) with using a sprayingmaterial in slurry form in Examples 8 to 12 and Comparative Example 6.The sprayed coating was formed, as the surface layer coating shown inTable 3, directly on the substrate (except for Example 8), or via theunderlaying coating (lower layer coating) that was formed by atmosphericplasma spraying on the substrate (Example 8). Crystalline phases of thelower layer coating used in Example 8 were identified by X-raydiffraction (XRD), and constituent crystals were analyzed. A surfaceroughness Ra, a thickness and a porosity were measured. The results areshown in Table 3. Detail of respective measurement or analysis isdescribed later.

The atmospheric plasma spraying was performed by a thermal sprayingmachine, SG-100, manufactured by Praxair S.T. Technology, Inc., underatmospheric pressure in normal pressure, and the suspension plasmaspraying was performed by a thermal spraying, machine 100HE,manufactured by Progressive Co., Ltd., under atmospheric suspensionplasma spraying in normal pressure. The conditions of atmospheric plasmaspraying and suspension plasma spraying for forming the sprayed coating(surface layer coating) are shown in Table 4.

Crystalline phases of the obtained sprayed coating (surface layercoating) were identified by X-ray diffraction (XRD), and constituentcrystals were analyzed. A diffraction angle (2θ(R⁺AL)) of a peak thatpositions at 0.05 to 0.5° (in difference) lower than the diffractionangle attributed to the maximum XRD diffraction peak of the rare earthaluminum monoclinic (R₄Al₂O₉) in the spraying material used. From theresults of quantification of yttrium and aluminum by X-ray fluorescenceanalysis, the ratio of yttrium and aluminum was calculated as therelative contents of the yttrium oxide (Y₂O₃) and the relative contentof the aluminum oxide (Al₂O₃) in the total of both contents. A surfaceroughness Ra, a thickness, a Vickers hardness HV 0.3, and a porositywere measured. Further, as corrosion resistance of the sprayed coatingand an amount of rare earth particles generated were evaluated by usingthe obtained sprayed member. The results are shown in Table 3. The XRDprofile in Example 8 is shown in FIG. 2. The results are shown in Table3. Detail of respective measurement, analysis or evaluation is describedlater.

TABLE 3 Example Comparative Example 7 8 9 10 11 12 4 5 6 2θ(RAL) (°)29.62 29.62 29.58 30.42 30.94 29.62 — — — Surface layer 2θ(R⁺AL) 29.5229.45 29.43 30.24 30.73 29.47 — — — coating (°) Crystalline Y₂O₃ Gd₂O₃Yb₂O₃ Y₂O₃ Y₂O₃ Y₃Al₅O₁₂ Y₂O₃ phase other Y₄Al₂O₉ Gd₄Al₂O₉ Yb₄Al₂O₉Y₄Al₂O₉ than (R⁺AL) Y₃Al₅O₁₂ Gd₃Al₅O₁₂ Yb₃Al₅O₁₂ Y₃Al₅O₁₂ by XRD Rareearth 89.9 91.3 86.3 93.7 92.1 91.5 100 57.7 100 oxide (wt %) Aluminum10.1 8.7 13.7 6.3 7.9 8.5 0 42.3 0 oxide (wt %) Surface 5.6 5 1.9 1.5 64.7 4.6 7.1 1.1 roughness Ra (μm) Thickness 300 50 100 100 100 150 200150 100 (μm) Vickers 820 920 770 650 730 850 490 700 600 hardness HV0.3Porosity (%) 1.6 0.7 0.5 0.9 0.6 0.8 3.8 3.3 0.1 Corrosion 1.8 1.5 2.12.8 2.4 1.7 1.9 4 3.3 resistance (average step) (μm) Rare earth 1.2 0.60.8 1.3 1.5 0.9 7.3 0.8 3.2 particles (μg/cm²) Lower Crystalline — Y₂O₃— — — — — — — layer phase coating by XRD Surface — 4.7 — — — — — — —roughness Ra (μm) Thickness — 150 — — — — — — — (μm) Porosity (%) — 2.2— — — — — — — Substrate Material Aluminum Aluminum Alumite + Aluminumalloy oxide alloy Aluminum alloy Abrasive grain #60 #60 #150 #150 #60#60 #60 #60 #150 size

TABLE 4 Example Comparative Example 7 8 9 10 11 12 4 5 6 Sprayingmaterial 1 2 3 4 5 6 1 2 3 Thermal spraying method APS SPS SPS SPS SPSSPS APS APS SPS Temperature of substrate (and 200 180 150 130 220 160100 120 160 lower layer coating) (° C.) Plasma gas Ar (L/mim) 25 180 180180 180 180 25 25 180 N₂ (L/mim) 0 70 70 70 70 70 0 0 70 H₂ (L/mim) 0 7070 70 70 70 0 0 70 He (L/mim) 21 0 0 0 0 0 21 21 0 Feed rate of sprayingmaterial 20 50 53 44 49 86 20 20 50 (g/min) Current (A) 900 407 407 407407 407 900 900 407 Voltage (V) 44 258 258 258 258 258 44 44 258 Power(kW) 40 105 105 105 105 105 40 40 105 Spraying distance (mm) 80 75 70 9065 75 80 80 75

[X-Ray Diffraction (XRD)]

The characteristic X-ray was Cu-Kα, and a diffraction profile wasobtained within a diffraction angle 2θ of 10° to 70°.

[BET Specific Surface Area]

The BET specific surface area was measured by a full automatic surfacearea analyzer, Macsorb HM model-1280, manufactured by Mountech Co., Ltd.

[Bulk Density]

The bulk density was measured by a power tester, PT-X, manufactured byHosokawa Micron Corporation.

[Ratio of Rare Earth Oxide and Aluminum Oxide]

Contents of rare earth and aluminum were measured by X-ray fluorescenceanalysis method, and based on the measured values, the ratio of them wascalculated as a ratio of the relative contents of the yttrium oxide(Y₂O₃) and the relative content of the aluminum oxide (Al₂O₃).

[Particle Size Distribution]

The volume-based particle size distribution was measured by a laserdiffraction method, and an average particle size D50 was evaluated.

[Viscosity of Slurry]

The viscosity of slurry was measured by a viscometer, Type TVB-10,manufactured by Toki Sangyo Co., Ltd., at a rotation speed of 60 rpm andfor a rotation time of 1 minute.

[Surface Roughness Ra]

The surface roughness Ra was measured by a surface roughness measuringinstrument, HANDYSURF E-35A, manufactured by Tokyo Seimitsu Co., Ltd.

[Coating Thickness]

The coating thickness was measured by an eddy current coating thicknesstester, LH-300J, manufactured by Kett Electric Laboratory.

[Vickers Hardness HV 0.3]

The surface of the sprayed coating of a test piece was processed to amirror surface having a surface roughness Ra of 0.1 μm. A Vickershardness HV 0.3 was measured at the processed mirror surface of the testpiece by a micro Vickers hardness meter, HMV-G, manufactured by ShimadzuCorporation, at a load of 2.942 N and for a holding time of 10 seconds.The results were evaluated as an average value of five points.

[Porosity]

A test piece was embedded in resin, and cut out at cross sectionsurface. The surface was processed to a mirror surface having a surfaceroughness Ra of 0.1 μm, then, a photograph of the surface was taken byan electron microscope (magnification: 1,000 times). After imaging infive view fields (imaging area per one visual field: 0.01 mm²), aporosity was quantified by an image analysis software “ImageJ” (publicsoftware by National Institutes of Health). A porosity was calculated asa percentage of the pore area with respect to the whole area of theimage, and the results were evaluated as an average value of five viewfields. The measurement of the porosity was specifically performedaccording to the following procedure.

(1) A test piece of the coating cut into a size of 9 mm×9 mm square and5 mm thick (including a substrate) is embedded into a resin.

(2) A cross section is mirror-polished (surface roughness Ra=0.1 μm).

(3) A cross-sectional photograph (backscattered electron image) with amagnification of 1,000 times is taken by SEM.

(4) A range for image processing of a cross-sectional photograph isspecified and trimming processing is performed, by using the imageanalysis software “ImageJ”.

(5) The processed image is converted to a grayscale image.

(6) As a setting of a threshold value of the image, a low-levelthreshold value is set to 0, and a high-level threshold value is set toa value at which all voids are colored red.

(7) The processed image is converted to a binarized image.

(8) The total area of the void portion is calculated.

(9) The length unit is set to pixels, and the total area (pixel) of thevoid portion is obtained.

(10) A threshold of the image is set such that a low-level threshold is0, and a high-level threshold is 255, then the whole area (pixel) of theimage is obtained.

(11) A porosity is calculated by dividing the total area (pixel) of thevoid portion by the whole area (pixel) the image.

[Test and Evaluation of Corrosion Resistance]

A surface of the sprayed coating (surface layer coating) of a test piece(sprayed member) was finished to a mirror surface having a surfaceroughness Ra of 0.1 μm. After preparing a portion covered with a maskingtape and an exposed portion of the coating, the test piece was set in anapparatus for reactive ion plasma test, and exposed to plasma underconditions of a plasma output of 440 W, gas spices of CF₄+20 vol % O₂, aflow rate of 20 sccm, a gas pressure of 5 Pa, and a test time of 8hours. To the test piece after the plasma exposure, a height of the stepcaused by corrosion between the portion covered with the masking tapeand the exposed portion of the coating was measured by a contact-typesurface profile measuring system, Dektak 3030, manufactured by BrukerNano Inc. The results of corrosion resistance were evaluated bycalculating an average value of four points. In the evaluation by thistest, the average value of the height of the steps (average height instep) is preferably up to 3.5 μm. When the average step height in stepis more than 3.5 μm, plasma etching resistance may not be exhibitedsufficiently for using in a plasma etching apparatus. The average stepheight in step is more preferably up to 3.2 μm, even more preferably upto 3 μm.

[Test and Evaluation of Amount of Rare Earth Particles Generated]

A test piece (sprayed member) was subjected to ultrasonic cleaning(output: 200 W, cleaning time: 30 minutes), dried, then, the test piecewas immersed into 20 mL of ultrapure water, and further subjected toultrasonic cleaning for 5 minutes. After the ultrasonic cleaning, thetest piece was taken out, and 2 mL of a 5.3 N nitric acid aqueoussolution was added into the ultrapure water after the ultrasoniccleaning to dissolve rare earth particles contained in the ultrapurewater. An amount of rare earth in the collected rare earth particles wasmeasured by ICP emission spectroscopy, and evaluated as an amount ofrare earth per surface area of the sprayed coating of the test piece. Inthe evaluation by this test, the amount of rare earth particles ispreferably up to 3 μg/cm². When the amount of the rare earth particlesis more than 3 μg/cm², generation of the particles is to many, and thesprayed member may not be withstood for use in a plasma etchingapparatus. The amount of rare earth particles is more preferably up to2.5 μg/cm², and even more preferably up to 2 μg/cm².

The sprayed coating (surface layer coating) obtained in Example 7 to 12has excellent plasma etching resistance (corrosion resistance) withreduced amount of rare earth particles generated by a reaction withcorrosion halogen-based gas plasma. The generation of rare earthparticles relates to the phenomenon that an aluminum halide evaporatesand does not remain as particles when the surface of a sprayed coatingis halogenated by halogen-based gas plasma, however, a rare earth halidegenerated remains as particles without evaporating. On the other hand,in terms of plasma etching resistance ability, rare earth-rich case issuperior to aluminum-rich case. Further, the generation of rare earthparticles relates to the fact that a rare earth-rich spraying materialhas few particles that cause particle contamination and form a roughcoating compared with an aluminum-rich spraying material.

The spraying material obtained in Example 1 to 6 has an intensity ratioI(R)/I(RAL) of at least 1. The spraying material can suitably form asprayed coating including a composite oxide (R⁺AL) having a rareearth-rich composition compared to the stoichiometric composition ofrare earth aluminum monoclinic (R₄Al₂O₉), in a rare earth oxide contentof 75 to 99 wt % and an aluminum oxide content of 1 to 25 wt %, asrelative contents of a rare earth oxide and an aluminum oxide (Al₂O₃)content. Particularly, since the value of S/ρ obtained by dividing thesurface area S by the bulk density ρ is in the range of 1 to 4, thespraying material has few particles that cause particle contaminationand form a rough coating. Therefore, from these results, it isrecognized that rare earth particles are less generated in such aspraying material, and the spraying material has an advantage forforming a sprayed coating having excellent plasma etching resistance(corrosion resistance).

Further, in the sprayed coating (surface layer coating) obtained inExample 7 to 12, the spraying material used has an XRD diffraction peakdetected at a diffraction angle that is 0.05 to 0.5° (in difference)lower than the diffraction angle attributed to the maximum XRDdiffraction peak of the rare earth aluminum monoclinic (R₄Al₂O₉).According to existence of the peak, it has been confirmed that thesprayed coating includes a composite oxide (R⁺AL) having a rareearth-rich composition compared to the stoichiometric composition ofrare earth aluminum monoclinic (R₄Al₂O₉), and having a structure suchthat Al atom sites in the rare earth aluminum monoclinic (R₄Al₂O₉) arepartially substituted with the rare earth (R) atoms. Further, it isrecognized that by inclusion of the composite oxide (R⁺AL) having such arare earth-rich composition, the spraying material obtained in Example 7to 12 has superior plasma etching resistance (corrosion resistance) withreduced amount of particles generated by a corrosive halogen-based gasplasma.

Japanese Patent Application No. 2019-076099 is incorporated herein byreference.

Although some preferred embodiments have been described, manymodifications and variations may be made thereto in light of the aboveteachings. It is therefore to be understood that the invention may bepracticed otherwise than as specifically described without departingfrom the scope of the appended claims.

1. A spraying material comprising a rare earth (R), aluminum and oxygen,the spraying material being a powder and comprising a crystalline phaseof a rare earth (R) aluminum monoclinic (R₄Al₂O₉) and a crystallinephase of a rare earth oxide (R₂O₃), wherein with respect to diffractionpeaks detected within a diffraction angle 2θ range from 10° to 70° by aX-ray diffraction method using the characteristic X-ray of Cu-Kα, thespraying material has diffraction peaks attributed to the rare earthoxide (R₂O₃) and diffraction peaks attributed to the rare earth (R)aluminum monoclinic (R₄Al₂O₉), and an intensity ratio I(R)/I(RAL) of anintegral intensity I(R) of the maximum diffraction peak attributed tothe rare earth oxide (R₂O₃) to an integral intensity I(RAL) of themaximum diffraction peak attributed to the rare earth aluminummonoclinic (R₄Al₂O₉) is at least
 1. 2. The spraying material of claim 1having a BET specific surface area S of at least 1 m²/g, and a bulkdensity ρ of up to 2 g/cm³.
 3. The spraying material of claim 2 having avalue S/ρ of 1 to 4, wherein the value S/ρ is obtained by dividing theBET specific surface area S by the bulk density ρ.
 4. The sprayingmaterial of claim 1 having a composition corresponding to a relativerare earth oxide (R₂O₃) content of 75 to 99 wt % and a relative aluminumoxide (Al₂O₃) content of 1 to 25 wt % in the total content of the rareearth oxide (R₂O₃) and the aluminum oxide (Al₂O₃), wherein the rareearth oxide (R₂O₃) content and the aluminum oxide (Al₂O₃) content are,respectively, calculated from the basis of an rare earth (R) content andan aluminum content in the spraying material.
 5. The spraying materialof claim 1, wherein the rare earth (R) is selected from the groupconsisting of yttrium (Y), gadolinium (Gd), terbium (Tb), dysprosium(Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), andlutetium (Lu).
 6. The spraying material of claim 1 having an averageparticle size D50 of 1 to 50 μm.
 7. A spraying slurry comprising thespraying material of claim 1, and a dispersion medium, wherein a contentof the spraying material in the spraying slurry is 10 to 70 wt %.
 8. Thespraying slurry of claim 7, wherein the dispersion medium is an aqueousdispersion medium.
 9. The spraying slurry of claim 7, further comprisinga dispersing agent.
 10. The spraying slurry of claim 7 having aviscosity of less than 15 mPa·s.
 11. A method of preparing a sprayingslurry comprising the steps of: forming a slurry by dispersing analuminum oxide in an aqueous solution of a rare earth salt; crystalizinga precursor containing the rare earth and aluminum, as a precipitate, byadding a precipitant to the slurry; collecting the precipitate by asolid-liquid separation; and firing the precursor containing the rareearth and aluminum under an oxygen-containing gas atmosphere.
 12. Amethod of forming a sprayed coating comprising the step of: forming thesprayed coating comprising a composite oxide containing a rare earth andaluminum, directly or via an underlaying coating on a substrate byplasma spraying with using the spray material of claim
 1. 13. A sprayedcoating comprising a rare earth (R), aluminum and oxygen, the sprayedcoating comprising a crystalline phase of a composite oxide containingthe rare earth (R) and aluminum, wherein the crystalline phase of acomposite oxide comprises a crystalline phase of a composite oxidehaving a rare earth-rich composition compared to the stoichiometriccomposition of rare earth aluminum monoclinic (R₄Al₂O₉), and having astructure such that Al atom sites in the rare earth aluminum monoclinic(R₄Al₂O₉) are partially substituted with the rare earth (R) atoms. 14.The sprayed coating of claim 13, further comprising a crystalline phaseof a rare earth oxide (R₂O₃).
 15. The sprayed coating of claim 13,further comprising at least one crystalline phase selected from thegroup consisting of a rare earth aluminum monoclinic (R₄Al₂O₉), a rareearth aluminum perovskite (RAlO₃), and a rare earth aluminum garnet(R₃Al₅O₁₂).
 16. The sprayed coating of claim 13 having a compositioncorresponding to a relative rare earth oxide (R₂O₃) content of 75 to 99wt % and a relative aluminum oxide (Al₂O₃) content of 1 to 25 wt % inthe total content of the rare earth oxide (R₂O₃) and the aluminum oxide(Al₂O₃), wherein the rare earth oxide (R₂O₃) content and the aluminumoxide (Al₂O₃) content are, respectively, calculated from the basis of anrare earth (R) content and an aluminum content in the sprayed coating.17. The sprayed coating of claim 13, wherein the rare earth (R) isselected from the group consisting of yttrium (Y), gadolinium (Gd),terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm),ytterbium (Yb), and lutetium (Lu).
 18. The sprayed coating of claim 13having a surface roughness Ra of up to 8 μm.
 19. The sprayed coating ofclaim 13 having a thickness of 10 to 500 μm.
 20. The sprayed coating ofclaim 13 having a Vickers hardness HV 0.3 of at least
 600. 21. Thesprayed coating of claim 13 having a porosity of up to 5%.
 22. A sprayedmember comprising the sprayed coating of claim 13 formed directly or viaan underlaying coating on a substrate.